Topographic mapping of retinal neurons in the european anchovy by nuclear staining and immunohistochemistry

Abstract

The anchovy retina is unique among vertebrates in being designed for polarization-contrast vision and has a marked cone area in the ventrotemporal quadrant for acute vision in the frontal field of view. Whereas cone topography and fine structure have been well examined in the European anchovy, the morphological organization of its inner retina is poorly understood so far. Using fluorescence staining of cell nuclei in combination with antibody stainings, the 3D pattern of cell nuclei was recorded coevally in all three retinal cell layers by confocal laser scanning microscopy, and the topographies of several neuron types were mapped separately across the retina. Cell classification and quantification succeeded for rods, cones, three types of horizontal cells (H1-3), rod and cone bipolars, amacrines, ganglion cells, and displaced amacrines as well as Müller cells; moreover, the morphology of H1 horizontal cells (calretinin-positive), rod bipolars (protein kinase C-positive), and a subtype of cone bipolars (parvalbumin-positive) is shown. Most cell types follow the cone topography, with a cell density maximum in the ventrotemporal quadrant (e.g., 730 cones, 2,800 cone bipolars, 230 GCL cells per 10(4) μm(2) ), showing their affiliation to the photopic system, except rods and rod bipolars (showing a cell density minimum in the cone area). The correlation of density maps of different cell types provides insight into convergence and divergence patterns in cone and rod pathways.

Intraretinal variability and specialization of cones in Japanese anchovy (Engraulis japonicus, Engraulidae)

“…This results in at least a three‐fold increase in the cell density and, according to our estimation, an almost twofold increase in spatial resolution. That agrees with the calculated cone ratios for the ventro‐temporal and central retina in northern and European anchovies (1: 3.5 and 1: 4, respectively) (O'Connell, ; Heß, ; Koch and Heß, ). The detectable distance of a 1 mm diameter prey estimated using the formula provided by Miyazaki and Kobayashi () is approximately 12–25 cm for the Japanese anchovy.…”

“…Small pieces were excised from certain regions of the same retina and subjected to morphological and microspectrophotometric investigations. The locations from which the material was resected corresponded to the retinal map of the Japanese anchovy (Miyazaki and Kobayashi, ) that is similar to retinal maps of other species of the same genus Engraulis (Heß et al, ; Koch and Heß, ; Novales Flamarique, ).…”

“…The interactions with the surrounding cells and with cells of the pigment epithelium make it possible to differentiate a “polycone unit” as structural formation of one long cone “…united to an outer segment lobe from each of the adjacent short cones” (Fineran and Nicol, ). Polycone units were found across the retinal regions in which the long and cones were located, including area temporalis in the ventro‐temporal zone characterized by a high density of cones and other retinal neurons (Heß et al, ; Koch and Heß, ). Here, the long cones are positioned sclerad in relation to the short cones, which results in unusual bi‐layered architecture of the whole cone layer.…”

Morphological characteristics of eyes and retinas of two sardines (Sardinops melanostictus and Etrumeus sadina, Clupeidae) and an anchovy (Engraulis japonicus, Engraulididae)

“…We should note that the cell densities reported in this study for anchovy and sardine are much lower than in previous studies (O'Connell, ; Koch et al, ; Koch and Heβ, ). In the two papers by Koch et al () on E. encrasicolu s and by O'Connell () on E. mordax and S. caerulea , the ganglion cell density is about five times higher than in this study.…”

“…In these three species, the topographical maps of the ganglion cell showed that the highest density area was localized at the ventrotemporal quadrant of the retina, that is, temporal of the optic cleft, and their visual “interest” was hypothesized to be directed frontally upward. Also in the European anchovy ( E. encrasicolus ), the highest ganglion cell density area was observed in the ventrotemporal quadrant, and a topographical resemblance was found between ganglion and cone cell distribution (Koch et al, ; Koch and Heβ, ). The density of cone cells across the retina was also measured in other anchovies and sardines ( S. caeruleus , Alosa sapidissima , E. mordax , and Anchoa compressa , O'Connell, ; Cetengraulis mysticetus and Anchovia macrolepidota , Heß, ), and all topographical maps showed a sharply defined area of high cone cell density in the ventrotemporal quadrant.…”